The present invention relates to a method for establishing a call in a telecommunications network, a telecommunications network, and a controlling device for packet networks. More particularly, the present invention relates to an optimized method, network, and device for facilitating packet network calls in mixed packet and TDM environments.
Modern communications networks generally carry two types of traffic or data. The first is the traffic which is transmitted by or delivered to a user or subscriber, and which is usually paid for by the user. That type of traffic is widely known as user traffic or subscriber traffic. The second is the traffic caused by network management applications in sending and receiving management data from network elements, known as management traffic.
In telecommunications, the management traffic is also known as signaling traffic. The term “signaling” refers to the exchange of signaling messages between various network elements such as database servers, local exchanges, transit exchanges, and user terminals. A well known protocol for transferring such signaling messages in public switched telephone networks (PSTN) is the Signaling System 7 (SS7), also referred to as Common Channel Signaling System 7 (CCS7).
The Signaling System 7 as specified by the International Telecommunication Union (ITU) in the Q.700-series standards provides for all signaling tasks in today's voice-oriented telecommunications networks. More specifically, SS7 provides for example for:                basic call setup, management, and tear down;        enhanced call features such as call forwarding, calling party name/number display, and automatic callback (call return);        accounting and billing;        database operations for services such as authentication, roaming, toll-free and special tariff services, and number portability;        network management for the SS7 network and its connections; and        non-call related signaling, allowing for services such as short message service (SMS), ISDN Supplementary Services and user-to-user signaling (UUS).        
With the advent of “next generation” packet based telecommunications networks, and internet protocol (IP) based networks in particular, new signaling and bearer protocols were developed by the ITU and other standards bodies such as IETF, ETSI, and 3GPP.
The functional architecture of such Next Generation Networks (NGN) seeks to provide a technology independent architecture for supporting multimedia services. The intention is to support a wide range of voice, data and video services while providing inter-working with the legacy PSTN (Public Switched Telephone Network) and cellular/wireless networks, also collectively referred to as time division multiplex (TDM) networks, and/or with legacy devices.
Presently, PSTN-type, or TDM, networks dominate the voice telephony globally. While the IP based networks and their telephony applications by means of voice over IP (VoIP) protocols are expanding, the PSTN-type networks—still adequate for providing reliable voice services—will only gradually lose their dominance. It is foreseen that the two network types will coexist and inter-work in numerous ways in the next decades.
In particular, the PSTN infrastructure will dominate long distance and international calls. Consequently, many of the rules and regulations established for PSTN operations will prevail in mixed environments. This is particularly true for uniquely addressing parties or their telecommunications equipment, respectively. While IP networks are capable of various forms of addressing a called party, for example by a symbolic name such as an email address or a SIP Uniform Resource Identifier, a PSTN is only capable of handling telephone numbers as laid out in numbering plans such as the ITUT E.164 international numbering plan.
If, for example, a PSTN subscriber wishes to establish a connection to a subscriber of an IP network, the PSTN subscriber has only one way of addressing the IP subscriber, that is, by dialing digits, even though the IP subscriber may have the name dialing capability. Therefore, IP subscribers who want to be able to receive calls from PSTN subscribers need to be assigned a regular PSTN directory number.
In another example, where a PSTN subscriber is represented within the IP network by a name, and the IP subscriber can address this PSTN subscriber by name, prior to presenting this call to a PSTN switch, the name has to be converted to digits. Of course, the PSTN subscriber may instead or additionally be addressed from within the IP network by regular PSTN directory number.
Consequently, if a first subscriber of a first IP network wishes to call second subscriber, it will be necessary for the first subscriber to use digits in order to route the call in the PSTN-dominated inter-working network arrangement. If the second subscriber is subscriber to a second IP network, then traversing the PSTN provides no benefit but rather limits the connection capabilities to the PSTN capability set, i.e. none of the advanced IP network features such as exchanging data, images or video will be available even though both subscribers are, in fact, IP subscribers.
There are various other scenarios where a connection between two IP subscribers inevitably and undesirably traverses a PSTN network section at least once.